Combustor

ABSTRACT

A vapor generator for a vapor cycle engine incorporates a toroidal tube bundle having a central combustion zone in which a rotary atomizer dispenses fuel for mixture with incoming air. A first fan draws air into the combustion zone for mixture with the fuel and a second fan associated with the rotary atomizer enhances the character of fluid flow in the combustion zone, particularly at low firing rates. First air passages adjacent the combustion chamber direct air flow into the combustion zone from above and below the atomized fuel. Second passages are situated to confront flow from the first passages.

v United States Patent [191 Sakhuja July 22, 1975 COMBUSTOR Ravinder K. Sakhuja, Jamaica Plain, Mass.

[75] Inventor:

[73] Assignee: Thermo Electron Corporation,

Waltham, Mass.

[22] Filed: Dec. 14, 1973 [21] Appl. No.: 425,037

[52] US. Cl 122/250 R; 122/3; 431/168 [51] Int. Cl. F22b 27/08 [58] Field of Search 122/3, 248, 249, 250 R, 122/367; 431/168 [56] References Cited UNITED STATES PATENTS 1,934,661 11/1933 Farerty 122/3 2,160,644 5/1939 Clarkson 122/250 2,417,929 3/1947 Hanson 431/168 X 2,620,864 12/1952 Ray 431/168 X 8/1967 Taylor 122/250 2/1971 Hoagland 122/250 Primary Examiner-Kenneth W. Sprague Attorney, Agent, or Firm-James L. Neal 57 ABSTRACT A vapor generator for a vapor cycle engine incorporates a toroidal tubebundle having a central combustion zone in which a rotary atomizer dispenses fuel for mixture with incoming air. A first fan draws air into the combustion zone for mixture with the fuel and a second fan associated with the rotary atomizer enhances the character of fluid flow in the combustion zone, particularly at low firing rates.

First air passages adjacent the combustion chamber direct air flow into the combustion zone from above and below the atomized fuel. Second passages are situated to confront flow from the first passages.

16 Claims, 2 Drawing Figures COMBUSTOR BACKGROUND OF THE INVENTION Vapor cycle engines, particularly Rankine cycle engines, afford an attractive alternate power supply to the more conventionally used power sources such as internal combustion engines and electric motors from the standpont of efficiency and emission characteristics. In many applications, however, it is desirable to minimize the size of the engine.

One of the largest components in a vapor cycle engine is the vapor generator. Attempts to reduce the size of the vapor generator must be balanced against effects on its performance and thereby performance of the overall engine system. Burnerboiler combinations in a flat circular configuration and incorporating a toroidal tube bundle with a central combustion chamber have been suggested. These require even fuel distribution in the combustion chamber, especially to provide good performance at low firing rates.

Accordingly, it is anobject of this invention to provide a compact vapor generator for a vapor cycle engine;

It is a further object of this invention to provide a compact, flat circular vapor generator for a vapor cycle engine which includes a toroidal tube bundle and a central combustion chamber in which a rotary fuel atomizer directs fuel radially outward from the center of the combustion chamber into a surrounding combustion zone from which products of combustion pass through the toroidal tube bundle;

It is an object of this invention to provide a compact vapor generator for a vapor cycle engine which operates efficiently and satisfactorily over a wide range of firing rates; and

It is also an object of this invention to provide a compact vapor generator for a vapor cycle engine which is characterized by a very low emission of air pollutants.

SUMMARY OF THE INVENTION This invention pertains to a vapor generator for a vapor cycle engine, preferably of a flat circular configuration, having a central combustion chamber surrounded by a tube bundle. The tube bundle conducts vapor engine working fluid into heat exchange relationship with products of combustion for heating the working fluid to vaporization for ultimate expansion to produce work. Centrally located within the combustion chamber is an atomizer for evenly distributing atomized fuel outward therefrom over substantially the entire combustion chamber.

Air is introduced to the combustion chamber from first and second plenum chambers located, respectively, above and below the combustion chamber. First and second openings are provided adjacent the atomizer to establish direct communication between the combustion chamber and the first and second plenum chambers, respectively. The plenum chambers are joined by connecting tubes bridging the combustion chamber. The connecting tubes are arranged in a path around the atomizer and communicate with the combustion chamber along their portions facing the atomizer so that communicating passages confront fluid flowing from the direction of the atomizer.

A blower, appropriately positioned, forces air from a location external of the vapor generator to the first and second plenum chambers and ultimately through the combustion chamber. Associated with the atomizer is a second blower within the combustion chamber for creating turbulence and/or recirculation of gases in the combustion chamber as described more fully below.

At high flow rates, when the first blower directs a large flow of air into the combustion chamber, air passes from the first and second plenum chambers, through the first and second openings, past the atomizer, into the combustion chamber. A quantity of air, which may be substantially equal to the quantity coming in through the first and second ports, enters the combustion chamber from the connecting tubes between the plenum chambers so that it is directed into the'combustion chamber in counterflow relationship (i.e., confronting relationship) to the atomized fuel and the air from the first and second ports. That is, the flow from the first and second ports as well as the flow from the atomizer is outward from the atomizer while the flow from the connecting tubes is inward toward the atomizer. The confronting flow creates substantial turbulence which produces efficient and stable combustion. From the combustion chamber, the general flow path forthe combustion products is outward over the tube bundle and thence out a suitable exhaust port. During this high flow mode of operation, the flow from the first blower is sufficiently large in comparison to the turbulence created by the second blower that the effect of the second blower is minimal.

In contrast to the high flow mode of operation, when the vapor generator is operating with minimum flow therethrough, as for example during idling, a different flow pattern is produced as a result of the secondary blower. During this low flow mode, flow from the primary blower is reduced so that the secondary blower produces a higher pressure drop in the combustion chamber than does the primary blower. Under these circumstances, air flowing from the first and second plenum chambers is drawn in through the first and second ports, respectively, as in the high flow mode. Air from the first and second ports joins fuel from the atomizer and is directed along a path outward from the atomizer. Since the secondary blower provides greater pressure drop in the combustion chamber than does the primary blower. Under these circumstances air flowing from the first and second plenum chambers is drawn in through the first and second ports, respectively, as in the high flow mode. Air from the first and second ports joins fuel from the atomizer and is directed along a path outward from the atomizer. Since the secondary blower provides greater pressure drop in the combustion chamber than does the primary blower, it enhances the outward flow from the combustion chamber. The combined pressure in the combustion chamber resulting from the second blower and the first blower is greater than the opposing pressure produced in the connecting tubes by the first blower. This condition produces flow reversal in the communicating passage between the connecting tubes and the combustion chamber so that a recirculation path is established in the combustion chamber. That is, gases from the combustion chamber travel through the connecting tube and reenter the first and second plenum chambers and are subsequently directed back into the combustion chamber. This cyclic flow continues with a certain portion of the fluid constantly cycling through the combustion chamber, the connecting tube and the first and second plenum chambers. A certain amount of flow (i.e. approximately that portion induced by the first blower) passes through the combustion chamber and over the tube bundle. Thus the flow across the tube bundle is maintained by the first blower at the low firing rate while the recycled flow induced by the second blower maintains a high degree of turbulence in the combustion chamber which produces good mixing and a resulting stable flame.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially broken away cross-sectional view of a preferred embodiment of this invention; and

FIG. 2 is a view taken along lines 22 of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS The flat, cylindrical vapor generator includes a combustion chamber 12 having centrally therein a rotary atomizer 14 for receiving fuel from a fuel supply and directing it into the combustion chamber. Surrounding the combustion chamber 12 is a generally toroidal tube bundle 16 for conducting a fluid to be vaporized into heat exchange relationship with products of combustion from the combustion changer. The combustion chamber 12 and tube bundle 16 are enclosed by a housing 18 forming a first plenum chamber 20 along one side of the combustion chamber and a second plenum chamber 22 along the opposite side thereof. The first and second plenum chambers feed air to the combustion chamber 12 through ports 24 and 26 respectively. The plenum chambers are also joined by a series of connecting tubes 28 arranged in a circular fashion within the combustion chamber around the atomizer 14. A ring 30 extends around the combustion chamber in communication with the connecting tubes 28 and forming an inwardly directed open face 32 covered by a screen 34. The atomizer l4 and the open face 32 of the ring are positioned so that the open face substantially surrounds the atomizer and confronts flow from both the atomizer and the ports 24 and 26.

A primary blower means 36 is positioned adjacent the first plenum chamber 20 along the side thereof opposite the combustion chamber 12. The blower means 36 comprises a fan 38 communicating with an air inlet 40 and an air passage 42 leading to the first plenum chamber 20. A second blower means 44 is associated with the atomizer l4 and mounted within the combustion chamber 12 for assisting in the maintenance of a turbulent condition therein, as will be hereinafter described. The fuel and air mixture in the chamber is ignited by ignition means 13.

There is also provided a control means 46 for controlling air supply to the combustion chamber 12 from the primary blower means 36. The control means 46 comprises essentially a two blade air shutter having a stationary blade 48 with openings 50 therein and a moveable blade 52 with openings 54 therein. Movement of the blade 52 relative to the blade 48 varies the size of a constriction formed between the passage 42 and the first plenum chamber by openings in the two blades.

Associated with the moveable shutter blade 52 are presser feet 100 for holding the moveable shutter blade closely adjacent the static shutter blade 48 to avoid the passage of gases through the air shutter except through the passageway formed by the openings 50 and 54. The presser feet 100 extend up through slots 102 and are held by plates 104. The feet are spring biased against the moveable blade 52 by means of springs 106. The

slots 102 extend in arcuate paths along the portion of the housing 18 in which they are formed to permit movement of the moveable blade 52, feet 100, springs 106 and plates 104 about the axis of rotation of the shaft 58. Cover plates 108 are provided to inhibit leakage of exhaust gases past the presser feet 100.

The atomizer 14 comprises a cup-shaped member 56 mounted upon a rotary shaft 58. The cup-shaped member 56 includes a bottom portion 60, a top portion 62 and intermediate the top and bottom portions a porous cylindrical member 64. Extending upwardly from the bottom 50 of the cup-shaped member 56 is an outwardly flared circular blade 66 within which a fuel receiver 68 is formed.

A fuel supply means 70 communicates with the receiver 68 from an external fuel supply source, not shown. The fuel supply means 70 includes a fuel line 72 having insulation 74 around the part thereof adjacent the combustion chamber 12 and a passage 76 extending downward beside the shaft 58 to a fuel manifold 78 from which openings 80 admit fuel to the receiver 68.

Mounted upon the top portion 62 and the bottom portion 60 of the cup-shaped member 56 is a series of blades 82 which form the second blower means 44. The second blower means 44, the atomizer 14 and the fan 38 are all mounted in common from the shaft 58. The

shaft is connected by means of a pulley 84 and a belt 86 to an electric motor 88.

The housing along one side of the tube bundle forms an exhaust conduit which communicates from adjacent the exhaust port 112 through an openings 114 and l 16 with a recirculation chamber 1 18. The recirculation chamber 118 communicates with the inlet 40 to the blower means 36 past the deflector 120.

Superimposed over the apparatus illustrated in FIG. 1 is a schematic showing a control system capable of providing a continuously variable firing rate. The control system incorporates a central control module 90 having an actuator 92 which provides a variable signal, proportional to the desired firing rate of the vapor generator. The central control module 90 communicates with the electric motor 88 for determining its speed and with a servo motor 94 for variably positioning the moveable blades of the air shutter 46. There is also provided a fuel flow control valve 96 responsive to the position of the air shutter 46 and an element 98 sensitive to the pressure drop across the air shutter for providing a feedback signal to the central control module 90. The

operation of the control means will be described below in connection with a description of the overall operation of the vapor generator 10.

Operation of the vapor generator 10 will now be described from a near maximum firing rate through the transition to a near minimum firing rate.

At maximum firing rates, the electric motor 88 drives the shaft 58 to rotate the fan 38, atomizer 14 and second blower means 44 at the same rotational speed. The fan draws air and some exhaust products from adjacent deflector through the inlet 40 and passes this inlet gas through the passage 42 and the open air shutter 46 to the first plenum chamber 20. Fromthe first plenum chamber 20 the inlet gas passes through the tubes 28 to the second plenum chamber 22. Inlet gas thus enters the combustion chamber through ports 24 and 26 and through the open space 32 of the ring 30. At near maximum firing rate the amount of gas entering the open face of the ring 30 may be approximately equal to the combined amount entering the ports 24 and 26.

Fuel is fed through the fuel supply means 70 and from the manifold 78 to the receiver 68. The manifold 78 and the openings 80 provide a uniform fuel distribution to the receiver 68 around its entire circumference. Rotation of the cup-shaped member 56 causes the fuel to advance along the receiver 68 and the blade 66 to the tip of the blade. The fuel preferably does not collect in the receiver but rather is present more or less as a film. The film of course gets thinner as the fuel passes along the divergent surface of the blade 66. The film of fuel is then flung from the tip of the blade 56 against the inner surface of member 64. The fuel is forced to permeate the porous member by centrifugal force and is thrown from its outer surface into the combustion chamber in the form of a very fine, atomized mist. The amount of atomization is determined by the porosity and rotational velocity of the member 64. One suitable porous material is sintered stainless steel having an average pore size of 12 microns. Variations in pososity over a range extending at least from 7 to microns is acceptable.

The blades 82 mounted on top 62 and bottom 60 of the rotating cup-shaped member 56 provide additional turbulence in the combustion chamber. Additional turbulence provided by the blades 82 is, however, relatively minimal at the maximum firing rate, as compared to the turbulence created by the inlet gases from the ports 24 and 26 confronting flow of gases introduced through the open face 32 of the ring 30. In other words, gases entering through the ports 24 and 26, as well as the fuel discharged from the atomizer 14, tend to flow along a path radially outward from the axis of rotation of the shaft 58 in confronting relationship to the gases flowing in a radially inward direction from the ring 30. These confronting gases mix and create a high degree of turbulence which produces efficient burning and low air pollutant production. The resulting combustion products then pass from the combustion chamber across the tube bundle 16 towards the exhaust port 112. The minimization of pollutant production is enhanced by recirculation of exhaust gases (eg 20% of the exhaust gases) from adjacent the exhaust port 112 through the exhaust conduit 110 and recirculation chamber 118 to the inlet 40. The tube bundle typically carries working fluid for a vapor cycle engine which enters in the liquid state from a condenser, is evaporated, and passes in its vapor state to an expander for the production of work.

When a reduction of the firing rate is desired, the actuator 92 is advanced to provide a signal for the central control module 90. The control module simultaneously reduces the speed of the motor 88 to reduce the rotational speed of the shaft 58 and provides a signal to the air shutter drive 94 to reposition the moveable blade 52 of the air shutter 46 to constrict the passage formed by openings 50 and 54. In response to movement of the blade 52, the fuel flow control valve 96 is adjusted to reduce fuel flow. The pressure differential sensing element 98 senses the pressure drop across the air shutter 46 and provides a feedback signal functionally related thereto for the central control module 90. This feedback signal may be used to further adjust the speed of motor 88.

The air shutter provides the dual function of accurately and predictably controlling the combustion gases fed by the fan 38 to the first plenum chamber 20 and also permits operation of the primary blower means 36 with a certain degree of independence of the second blower means 44 even though they are mounted on the same shaft. That is, when the air shutter 46 is full open the fan 38 induces flow of an air mass through the combustion chamber 12 substantially in excess of the mass which the blades 82 are capable of moving when they are mounted directly on the same shaft as the fan 38 and therefore rotatable at the same rotational speed. However, when the air shutter 46 is advanced toward its closed position, flow therethrough is restricted so that the effect of the blades 82 in the combustion chamber exceeds that of the fan 38. In operation, with both fan 38 and blades 82 mounted from the same shaft, it has been found advantageous to adjust the air shutter with changein firing rate so that. a pressure drop of 2 inches of water is maintained across the air shutter 46. Vanes 115 block circumferential flow paths to maintain flow substantially along radial lines.

Having described the function of the air shutter, it can now be appreciated that as the firing rate is decreased the flow into the combustion chamber of both fuel and air is also decreased. The rotational speed of the blades 82 decreases but, because the gases flowing to the first and second plenum chambers 20 and 22 is reduced by both reduction in speed of the fan 38 and reduction in the passage formed by the openings 50 and 54, the effect of the blades 82 upon pressure and turbulence conditions in the combustion chamber 12 begins to increase relative to the effects of the fan 38. Accord ingly, as the firing rate is' being reduced, the blades 82 pressurize the combustion chamber to a level which exceeds the pressure in the first and second plenum chambers 20 and 22. When this occurs, flow reversal in the ring 30 occurs and gases pass from the combustion chamber through the ring 30 and connecting tubes 28 to the plenum chambers 20 and 24. Circulation continues from the plenum chambers through the ports 24 and 26 back to the combustion chamber 12. The recirculation pattern thus established continues as long as the pressure in the combustion chamber 12 exceeds the pressure in the plenum chambers. Therefore, even when a very low volume of gases are passing through the vapor generator 10 from the inlet 40 to the exhaust 112, a high degree of circulation and turbulence is maintained in the combustion chamber by the blade 82. This high degree of turbulence continuously maintains stable burning conditions characterized by low pollutant production. Toiincrease the firing rate, the actuator 92 is advanced inthe reverse direction and the system then begins to reverse the operations just described.

It is appropriate to note at this point that the air shutter 46 could as well be on the opposite side of the fan 38, adjacent the inlet 40. Further, the action of the air shutter, insofar as it reduces the effect of the fan 38 in the combustion chamberrelative to the effect of the blades 48, can be achieved by mounting the second blower means 44 and the primary blower means 36 on separate shafts. When mounted upon separate shafts, the two blowers can operate at different rotational speeds. Their relative effect in:the combustion chamart will recognize that changes may be made without departing from the scope of the invention.

I claim:

1. In a vapor generator having a combustor adapted for use with a circumscribing tube bundle which conducts fluid to be vaporized into heat exchange relationship with combustion products, the combination comprising:

a. means forming first and second plenum chambers spaced from and facing each other to define a combustion chamber therebetween, said plenum chambers being adapted to receive a flow of precombustion gases for introduction to the combustion chamber;

b. a liquid fuel atomizer centrally located within the combustion chamber for directing fuel outward therefrom toward substantially the entire periphery of the combustion chamber, the periphery being adapted to receive the tube bundle;

c. means forming opposed openings centrally of the combustion chamber for establishing fluid communication between the combustion chamber and the first and second plenum chambers, said openings therefore being so arranged that fluid entering the combustion chamber therethrough. tends to flow outward therefrom toward the periphery of the combustion chamber;

a plurality of passages extending through the combustion chamber and connecting the first and second plenum chambers to each other, said passages being arranged intermediate the central portion of the combustion chamber and the tube bundle and along a path surrounding the central portion of the combustion chamber; and e. means forming openings in the surfaces of said passages facing the central portion of said combustion chamber for establishing communication between v 3. In a vapor generator having a combustor adapted for use with a circumscribing tube bundle which conducts fluid to be vaporized into heat exchange relationship with combustion products, the combination comprising:

a. means forming first and second plenum chambers spaced from and facing each other to define a combustion chamber therebetween, said plenum chambers being adapted to receive a flow of precombustion gasses for introduction to the combustion chamber;

b; a liquid fuel atomizer centrally located within the combustion chamber for directing fuel outward therefrom toward substantially the entire periphery of the combustion chamber, the periphery being adapted to receive the tube bundle;

0. means forming opposed openings centrally of the combustion chamber'for establishing fluid communication between the combustion chamber and the first and second plenum chambers, said openings therefore being so arranged that fluid entering the combustion chamber therethrough tends to flow outward therefromtoward the periphery of the combustion chamber;

d. a plurality of connecting passages extending.

through the combustion chamber connecting the first and second plenum chambers, said passages being arranged intermediate the central portion of the combustion chamber and the tube bundle along a path surrounding the central portion of the combustion chamber;

e. opening means within the combustion chamber communicating with the connecting passages and facing inward toward and confronting the central portion of the combustion chamber;

f. a blower mounted centrally of the combustor, adjacent the atomizer, for assisting in the production of an outward flow of fluid from the central portion of the combustion chamber; and t g. means controlling the flow of precombustion gasses to the combustion chamber for decreasing the pressure in the connecting passages relative to the pressure in the combustion chamber as firing rate decreases, whereby, when combustion chamber pressure is less than connecting passage pressure, flow along a path through the connecting passages and the opening means from the plenum chambers to the combustion chamber is established and confronts flow along an outward path from the central portion of the combustion chamber and, when combustion chamber pressure exceeds connecting passage pressure, flow through the opening means is reversed so that fluid from the combustion chamber reenters the plenum chambers through the connecting passages.

4. The combination chamber according to claim 1 wherein said atomizer comprises a cylindrical, porous wall mounted for rotation about an axis central of the combustion chamber and means for feeding fuel to the drical wall including a fuel impervious barrier mounted for rotating with the wall, the barrier forming a peripheral edge from which fuel is projected onto the inner surface of the wall by centrifugal force.

6. In a vapor generator having a combustor adapted for use with a circumscribing tube bundle which conducts fluid to be vaporized into heat exchange relationship with combustion products, the combination comprising: v

a. means forming first and second plenum chambers spaced from and facing each other to define a combustion chamber therebetween, said plenum chambers being adapted to receive a flow of precombustion gasses for introduction to the combustion chamber;

b. a liquid fuel atomizer centrally located within the combustion chamber for directing fuel outward therefrom toward substantially the entire periphery of the combustion chamber, the periphery being adapted to receive the tube bundle;

means forming opposed openings centrally of the combustion chamber for establishing fluid cornmunication between the combustion chamber and the first and second plenum chambers, said openings therefore being so arranged that fluid entering the combustion chamber therethrough tends to flow outward therefrom toward the periphery of the combustion chamber;

d. a plurality of passages extending through the combustion chamber and connecting the first and second plenum chambers, said passages being arranged intermediate the central portion of the combustion chamber and the periphery of the combustion chamber and along a path surrounding the central portion of the combustion chamber;

e. opening means within the combustion chamber communicating with the connecting passages and facing inward toward and confronting the central portion of the combustion chamber; and

means for exhausting products of combustion and recirculation means for conducting a portion of the combustion products from adjacent the exhaust means to the plenum chambers.

7. The combination according to claim 2 wherein the atomizer comprises a rotary fuel distributor for directing fuel into the combustion chamber by centrifugal force.

8. The combination according to claim 7 wherein the second blower is mounted upon the rotary fuel distributor.

9. A vapor generator including in combination a toroidal boiler tube bundle circumscribing a burner, the vapor generator comprising a rotating shaft coincident with the toroidal axis of the tube bundle, a first blower on a first end of the shaft for drawing air into the burner, an atomizer on a second end of the shaft for atomizing fuel prior to combustion, a combustion chamber concentric with and surrounding the atomizer for combusting a fuel and air mixture, a flow control means defining first and second paths for circulating air in the combustion chamber, the first path being radially outward from the toroidal axis and the second path being directed radially inward toward the toroidal axis for maintaining turbulence in the combustion chamber and thereby creating an efficient, clean combustible mixture; wherein the flow control means comprises a first plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the first blower is mounted for receiving air from the first blower, a second plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the rotary atomizer is mounted for accepting air from the first plenum chamber, a series of spaced connecting passages surrounding the toroidal axis and extending through the combustion chamber from the first plenum chamber to the second plenum chamber for transmitting air from the first plenum chamber to the second plenum chamber.

10. A vapor generator including in combination a toroidal boiler tube bundle circumscribing a burner, the vapor generator comprising a rotating shaft coincident with the toroidal axis of the tube bundle, a first blower on a first end of the shaft for drawing air into the burner, an atomizer on a second end of the shaft for atomizing fuel prior to combustion, a combustion chamber concentric with and surrounding the atomizer for combusting a fuel and air mixture, a flow control means defining first and second paths for circulating air in the combustion chamber, the first path being radially outward from the toroidal axis and the second path being directed radially inward toward the toroidal axis for maintaining turbulence in the combustion chamber and thereby creating an efficient, clean combustible mixture; wherein the flow control means comprises a first plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the first blower is mounted for receiving air from the first blower, a second plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the rotary atomizer is mounted for accepting air from the first plenum chamber, a series of spaced connecting tubes surrounding the toroidal axis and extending from the first plenum chamber to the second plenum chamber for transmitting air from the first plenum chamber to the second plenum chamber, a ring surrounding the toroidal axis and communicating on its radially outward side with the series of connecting tubes and forming openings on its radially inward side for communication with the combustion chamber and confronting the atomizer, a second blower attached to the shaft internal of the combustion chamber and in close proximity to the atomizer for inducing air flow radially outward from the atomizer and into the combustion chamber.

11. A vapor generator as defined in claim 10 wherein the flow control means further comprises means for regulating the air supply to the first plenum chamber from the first blower to increase the air pressure within the connecting tubes as the air flow rate increases in coordination with increase in the fuel flow rate whereby the direction of air flow through the ring is radially inward when the air pressure in the connecting tube is greater than the air pressure created in the combustion chamber.

12. A vapor generator as defined in claim 11 wherein the regulating means regulates the air supply to the first plenum chamber from the first blower to decrease the air pressure within the connecting tubes as the air flow rate decreases in coordination with a decrease in the fuel flow rate, whereby the direction of air flow through the ring reverses when the air pressure in the connecting tube falls below the air pressure created in the combustion chamber by the second blower.

13. A vapor generator as defined in claim 12 wherein, when pressure in the connecting tube falls below pressure in the combustion chamber, air circulates from the combustion chamber through the ring, into the connecting tubes, through the first and second plenum chambers, and back to the combustion chamber.

14. A vapor generator including in combination a toroidal boiler tube bundle circumscribing a burner, the vapor generator comprising a rotating shaft coincident with the toroidal axis of the tube bundle, a first blower on a first end of the shaft for drawing air into the burner, an atomizer on a second end of the shaft for atomizing fuel prior to combustion, a combustion chamber concentric with and surrounding the atomizer for combusting a fuel and air mixture, a flow control means defining first and second paths for circulating air in the combustion chamber, the first path being radially outward from the toroidal axis and the second path being directed radially inward toward the toroidal axis for maintaining turbulence in the combustion chamber and thereby creating an efficient, clean combustible mixture; wherein the atomizer comprises a fuel line for feeding fuel into the atomizer, a rotary receptacle for receiving fuel from the fuel line defining a peripheral edge for dispensing radially outward at a high velocity na] of the combustion chamber in close proximity to the atomizer for inducing air flow radially outward from the atomizer into the combustion chamber.

16. A vapor generator as defined in claim 15 further comprising means establishing auxiliary fluid communication paths between the combustion chamber and both the first and second plenum chambers. 

1. In a vapor generator having a combustor adapted for use with a circumscribing tube bundle which conducts fluid to be vaporized into heat exchange relationship with combustion products, the combination comprising: a. means forming first and second plenum chambers spaced from and facing each other to define a combustion chamber therebetween, said plenum chambers being adapted to receive a flow of precombustion gases for introduction to the combustion chamber; b. a liquid fuel atomizer centrally located within the combustion chamber for directing fuel outward therefrom toward substantially the entire periphery of the combustion chamber, the periphery being adapted to receive the tube bundle; c. means forming opposed openings centrally of the combustion chamber for establishing fluid communication between the combustion chamber and the first and second plenum chambers, said openings therefore being so arranged that fluid entering the combustion chamber therethrough tends to flow outward therefrom toward the periphery of the combustion chamber; d. a plurality of passages extending through the combustion chamber and connecting the first and second plenum chambers to each other, said passages being arranged intermediate the central portion of the combustion chamber and the tube bundle and along a path surrounding the central portion of the combustion chamber; and e. means forming openings in the surfaces of said passages facing the central portion of said combustion chamber for establishing communication between the combustion chamber and the connecting passages, said openings confronting the central portion of the combustion chamber.
 2. The combination according to claim 1 further comprising a blower mounted centrally of the combustor, adjacent the atomizer, for assisting in the production of an outward flow of fluid from the central portion of the combustion chamber.
 3. In a vapor generator having a combustor adapted for use with a circumscribing tube bundle which conducts fluid to be vaporized into heat exchange relationship with combustion products, the combination comprising: a. means forming first and seCond plenum chambers spaced from and facing each other to define a combustion chamber therebetween, said plenum chambers being adapted to receive a flow of precombustion gasses for introduction to the combustion chamber; b. a liquid fuel atomizer centrally located within the combustion chamber for directing fuel outward therefrom toward substantially the entire periphery of the combustion chamber, the periphery being adapted to receive the tube bundle; c. means forming opposed openings centrally of the combustion chamber for establishing fluid communication between the combustion chamber and the first and second plenum chambers, said openings therefore being so arranged that fluid entering the combustion chamber therethrough tends to flow outward therefrom toward the periphery of the combustion chamber; d. a plurality of connecting passages extending through the combustion chamber connecting the first and second plenum chambers, said passages being arranged intermediate the central portion of the combustion chamber and the tube bundle along a path surrounding the central portion of the combustion chamber; e. opening means within the combustion chamber communicating with the connecting passages and facing inward toward and confronting the central portion of the combustion chamber; f. a blower mounted centrally of the combustor, adjacent the atomizer, for assisting in the production of an outward flow of fluid from the central portion of the combustion chamber; and g. means controlling the flow of precombustion gasses to the combustion chamber for decreasing the pressure in the connecting passages relative to the pressure in the combustion chamber as firing rate decreases, whereby, when combustion chamber pressure is less than connecting passage pressure, flow along a path through the connecting passages and the opening means from the plenum chambers to the combustion chamber is established and confronts flow along an outward path from the central portion of the combustion chamber and, when combustion chamber pressure exceeds connecting passage pressure, flow through the opening means is reversed so that fluid from the combustion chamber reenters the plenum chambers through the connecting passages.
 4. The combination chamber according to claim 1 wherein said atomizer comprises a cylindrical, porous wall mounted for rotation about an axis central of the combustion chamber and means for feeding fuel to the inner cylindrical surface of the wall for projection radially outward in all directions through the wall by centrifugal force.
 5. The combination chamber according to claim 4 further comprising a fuel receiver internal of the cylindrical wall including a fuel impervious barrier mounted for rotating with the wall, the barrier forming a peripheral edge from which fuel is projected onto the inner surface of the wall by centrifugal force.
 6. In a vapor generator having a combustor adapted for use with a circumscribing tube bundle which conducts fluid to be vaporized into heat exchange relationship with combustion products, the combination comprising: a. means forming first and second plenum chambers spaced from and facing each other to define a combustion chamber therebetween, said plenum chambers being adapted to receive a flow of precombustion gasses for introduction to the combustion chamber; b. a liquid fuel atomizer centrally located within the combustion chamber for directing fuel outward therefrom toward substantially the entire periphery of the combustion chamber, the periphery being adapted to receive the tube bundle; c. means forming opposed openings centrally of the combustion chamber for establishing fluid communication between the combustion chamber and the first and second plenum chambers, said openings therefore being so arranged that fluid entering the combustion chamber therethrough tends to flow outward therefrom toward the periphery of the combustion chamber; d. a plurality of passages exteNding through the combustion chamber and connecting the first and second plenum chambers, said passages being arranged intermediate the central portion of the combustion chamber and the periphery of the combustion chamber and along a path surrounding the central portion of the combustion chamber; e. opening means within the combustion chamber communicating with the connecting passages and facing inward toward and confronting the central portion of the combustion chamber; and f. means for exhausting products of combustion and recirculation means for conducting a portion of the combustion products from adjacent the exhaust means to the plenum chambers.
 7. The combination according to claim 2 wherein the atomizer comprises a rotary fuel distributor for directing fuel into the combustion chamber by centrifugal force.
 8. The combination according to claim 7 wherein the second blower is mounted upon the rotary fuel distributor.
 9. A vapor generator including in combination a toroidal boiler tube bundle circumscribing a burner, the vapor generator comprising a rotating shaft coincident with the toroidal axis of the tube bundle, a first blower on a first end of the shaft for drawing air into the burner, an atomizer on a second end of the shaft for atomizing fuel prior to combustion, a combustion chamber concentric with and surrounding the atomizer for combusting a fuel and air mixture, a flow control means defining first and second paths for circulating air in the combustion chamber, the first path being radially outward from the toroidal axis and the second path being directed radially inward toward the toroidal axis for maintaining turbulence in the combustion chamber and thereby creating an efficient, clean combustible mixture; wherein the flow control means comprises a first plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the first blower is mounted for receiving air from the first blower, a second plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the rotary atomizer is mounted for accepting air from the first plenum chamber, a series of spaced connecting passages surrounding the toroidal axis and extending through the combustion chamber from the first plenum chamber to the second plenum chamber for transmitting air from the first plenum chamber to the second plenum chamber.
 10. A vapor generator including in combination a toroidal boiler tube bundle circumscribing a burner, the vapor generator comprising a rotating shaft coincident with the toroidal axis of the tube bundle, a first blower on a first end of the shaft for drawing air into the burner, an atomizer on a second end of the shaft for atomizing fuel prior to combustion, a combustion chamber concentric with and surrounding the atomizer for combusting a fuel and air mixture, a flow control means defining first and second paths for circulating air in the combustion chamber, the first path being radially outward from the toroidal axis and the second path being directed radially inward toward the toroidal axis for maintaining turbulence in the combustion chamber and thereby creating an efficient, clean combustible mixture; wherein the flow control means comprises a first plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the first blower is mounted for receiving air from the first blower, a second plenum chamber extending radially outward from the shaft and located adjacent the end of the shaft onto which the rotary atomizer is mounted for accepting air from the first plenum chamber, a series of spaced connecting tubes surrounding the toroidal axis and extending from the first plenum chamber to the second plenum chamber for transmitting air from the first plenum chamber to the second plenum chamber, a ring surrounding the toroidal axis and communicating on its radially outward side with the series of connecting Tubes and forming openings on its radially inward side for communication with the combustion chamber and confronting the atomizer, a second blower attached to the shaft internal of the combustion chamber and in close proximity to the atomizer for inducing air flow radially outward from the atomizer and into the combustion chamber.
 11. A vapor generator as defined in claim 10 wherein the flow control means further comprises means for regulating the air supply to the first plenum chamber from the first blower to increase the air pressure within the connecting tubes as the air flow rate increases in coordination with increase in the fuel flow rate whereby the direction of air flow through the ring is radially inward when the air pressure in the connecting tube is greater than the air pressure created in the combustion chamber.
 12. A vapor generator as defined in claim 11 wherein the regulating means regulates the air supply to the first plenum chamber from the first blower to decrease the air pressure within the connecting tubes as the air flow rate decreases in coordination with a decrease in the fuel flow rate, whereby the direction of air flow through the ring reverses when the air pressure in the connecting tube falls below the air pressure created in the combustion chamber by the second blower.
 13. A vapor generator as defined in claim 12 wherein, when pressure in the connecting tube falls below pressure in the combustion chamber, air circulates from the combustion chamber through the ring, into the connecting tubes, through the first and second plenum chambers, and back to the combustion chamber.
 14. A vapor generator including in combination a toroidal boiler tube bundle circumscribing a burner, the vapor generator comprising a rotating shaft coincident with the toroidal axis of the tube bundle, a first blower on a first end of the shaft for drawing air into the burner, an atomizer on a second end of the shaft for atomizing fuel prior to combustion, a combustion chamber concentric with and surrounding the atomizer for combusting a fuel and air mixture, a flow control means defining first and second paths for circulating air in the combustion chamber, the first path being radially outward from the toroidal axis and the second path being directed radially inward toward the toroidal axis for maintaining turbulence in the combustion chamber and thereby creating an efficient, clean combustible mixture; wherein the atomizer comprises a fuel line for feeding fuel into the atomizer, a rotary receptacle for receiving fuel from the fuel line defining a peripheral edge for dispensing radially outward at a high velocity the fuel by centrifugal force, a porous cylinder mounted for rotation with the receptacle and concentric with and surrounding the peripheral edge for accepting fuel therefrom and directing the fuel radially outward into the combustion chamber by centrifugal force in an atomized form.
 15. A vapor generator as defined in claim 9 further comprising a second blower attached to the shaft internal of the combustion chamber in close proximity to the atomizer for inducing air flow radially outward from the atomizer into the combustion chamber.
 16. A vapor generator as defined in claim 15 further comprising means establishing auxiliary fluid communication paths between the combustion chamber and both the first and second plenum chambers. 